The present disclosure relates to a fusing system. More particularly, the disclosure relates to a fusing system having external electromagnetic induction heating.
Electrophotographic printing and copying devices typically are provided with fusing systems that serve to thermally fuse a toner image onto a recording medium, such as a sheet of paper. Such fusing systems normally comprise a heated fuser roller and a heated pressure roller that presses against the fuser roller to form a nip in which the fusing occurs. The fuser and pressure rollers often comprise hollow tubes coated with thick layers of high temperature rubber. The hollow rollers enclose internal heat sources that uniformly irradiate the inner surfaces of the rollers. Through this irradiation, the inner surfaces are heated and this heat diffuses to the outer surfaces of the fuser and pressure rollers until they reach a temperature sufficient to melt the toner (e.g., approximately between 160xc2x0 C. to 190xc2x0 C.).
The fuser roller and the pressure roller rotate in opposite directions and are urged together so as to form a nip that compresses the outer high temperature rubber layers of the rollers. The compression of these layers increases the width of the nip, which increases the time that the recording medium resides in the nip. The longer the dwell time in the nip, the larger the total energy that the toner and recording medium can absorb to melt the toner. Within the nip, the toner is melted and fused to the medium by the pressure exerted on it by the two rollers. After the toner has been fused, the recording medium is typically forwarded to a discharge roller that conveys the medium to a discharge tray.
In the fusing system described above, a tungsten filament halogen lamp or thin film heater is typically used as the heat source. Unfortunately, the high thermal mass of the rollers and the high thermal resistance of the outer rubber layers of the rollers require a relatively long duration of time to reach operating temperature. Therefore, a user of the printing, copying, or facsimile device can be prevented from quickly utilizing the device. Although the rate that energy is applied to the fusing rollers can be increased, there are practical limits to the power available from a 120 volt, 15 or 20 ampere branch circuit.
In recent years, there has been a drive toward reducing warm-up time without increasing energy use. To that end, fusing systems have been proposed that utilize induction heating. These systems typically comprise an induction heating element that is disposed inside a hollow fuser roller constructed of a thin metal tube. In such systems, the coil of the induction heating element is placed in close proximity with the inner surface of the fuser roller to generate a high frequency magnetic field that induces eddy currents within the roller that, in turn, create heat.
Induction heating in this manner provides several advantages over more conventional heating methods. First, induction heating quickly elevates the temperature of the low thermal mass of the thin metal fuser roller yet generates heat only sparingly as compared with indirect heating with a halogen lamp. Second, induction heating apparatuses have greater useful lives in that sliding contact is not required between the coil and the inner surface of the fuser roller as is required of thin film heaters. Third, induction heating provides greater control over temperature because the reduced thermal mass and decreased transport lag allows the system to respond more quickly to thermal loads.
Although use of induction heating provides the advantages described above, there are disadvantages associated with present fusing system designs that incorporate induction heating. Most particularly, placement of the induction heating element within the fuser roller increases the total cost of ownership of the machine. First, current designs increase manufacturing costs in that inclusion of an induction heating element within the fuser roller greatly increases the complexity of the fuser roller design. Second, inclusion of the induction heating element within the fuser roller increases machine maintenance costs in that as is known in the art, conventional fusing systems must be periodically replaced due to failure of the outer surfaces of the rollers. With current designs, the induction heating element contained within the fuser roller and its associated temperature sensor and electrical connectors are discarded along with the fuser roller because of their integration with the roller. In that these components are expensive, it is wasteful to discard them in this manner, particularly because these components have a very low failure rate and normally would last the entire useful life of the print/copy engine.
From the foregoing, it can be appreciated that it would be desirable to have a fusing system that uses electromagnetic heating but which is less costly to manufacture and which comprises a permanent part of the machine in which is used.
The present disclosure relates to a fusing system for fusing toner to a recording medium. The fusing system comprises a fuser roller including a metal layer, a pressure roller in contact with the fuser roller, and an external induction heating element.
In addition, the disclosure relates to a method for heating a fuser roller of a fusing system. The method can be summarized by the following steps: positioning an external induction heating element in close proximity to the outer surface of the fuser roller, delivering high frequency current to a coil of the external induction heating element to create a magnetic flux, and directing the magnetic flux toward the fuser roller so as to induce eddy currents within a metal layer of the fuser roller that generate heat within the roller.
The features and advantages of the invention will become apparent upon reading the following specification, when taken in conjunction with the accompanying drawings.